Exactly as it states. If you have a really high RC, such that the chassis is 'hanging' from it, you could get the CG significantly below the RC. I think this would cause 'backwards' roll, the chassis would roll towards the inside of corner...

...so two wheels up front, one in back, would it lean like a bike? Or would you smash into a tree before finding out?

I haven't found much info on this idea, so it seems it is either very bad, or untested. Probably a bit of both.

I'm pretty sure that I've seen some pedal powered recumbent trikes that worked that way although some quick googleFU didn't show what I was looking for. The Trailmate Funcycle ( http://www.trailmate.com/productFunCycle.cfm ) is sort of that way but, again, was not exactly like what I've seen before.

I'm not aware of any tilting, road going vehicle with the cg below the rc.

On trikes and motorcycles where the entire vehicle leans, the rc is at ground level. Sport bikes typically have higher cgs which make it easier to lean back and forth.

On trikes where only part of the machine leans, such as GM's Lean machine, the roll center axis of the pivoting section is a line drawn between the tire at the contact patch and the pivot point, which is typically at axle height.

If only the passenger compartment pivots, the roll center of the passenger compartment is typically at axle height, below the passenger compartment cg.

Also then, in theory, if you could put the RC at the *same* height as the CG and keep it there, you would have zero body roll?

Yes and no.

You actually have 2 roll centers, the theoretical one obviously everyone raves on about and the other one which is very real and is at the contact patch of your 2 outside tyre's (although not necessarily evenly distributed depending on variables).

Eventually if you have enough grip, your CG is high enough and/or your track is narrow, centrifugal force will eventually roll the CG over the tyre's contact patch, you will initially have roll as the inside lifts and gravity simply compresses the outside suspension (depending on spring rate of course) next step of course is the consummate body roll

A motorcycle's RC is roughly 1" off the ground due to tyre distortion but that's just semantics, contact patch is a good enough description.

The point of tilting is to be able to easily shift the cg to the inside of the corner, allowing for a narrower track and reduced frontal area without tipping over in a corner.

The cg below the rc does just the opposite, but doesn't require input to stay upright when stopped, though I fail to see the point of such a system.

Along with a lower cg comes reduced ground clearance for tilting.

Cheapracer, I don't think Formula 1 cars tilt or have much suspension travel.

TRX, now that you mention it, I do recall having seen a really old racer that had bike tires and would tilt and also a newer German concept. We are talking about trikes and where the cg needs to be relative to the rc to tilt properly.

Tom17, keeping the rc at the cg (not easy) would prevent roll up to the roll over point, but having the rc high to meet the cg also causes poor camber gain and jacking.

Cheapracer, I don't think Formula 1 cars tilt or have much suspension travel.

Indeed they don't. They have a minor "stagecoach" effect to offset chassis roll to help keep the car's chassis low and level for the all important ground effects.

Miatav8,MstrASE,A&P,F wrote:

having the rc high to meet the cg also causes poor camber gain and jacking.

Entirely dependent on suspension type/design.

Miatav8,MstrASE,A&P,F wrote:

TRX, now that you mention it, I do recall having seen a really old racer that had bike tires and would tilt and also a newer German concept. We are talking about trikes and where the cg needs to be relative to the rc to tilt properly.

Exactly as it states. If you have a really high RC, such that the chassis is 'hanging' from it, you could get the CG significantly below the RC. I think this would cause 'backwards' roll, the chassis would roll towards the inside of corner...

...so two wheels up front, one in back, would it lean like a bike? Or would you smash into a tree before finding out?

Ok, I got it now, sorry for my waywardness.

I now see what you mean, you don't mean a titling trike you mean a trike that "stagecoaches".

Stagecoache's with luggage on the roof and the driver sitting so high have a very high CG so to combat this the manufacturers have the coach suspension pivots (RC) as high as practical to stop them falling over and keep the coach level for passengers comfort. When a coach only has people and no luggage the coach's CG is below the coaches RC so the lower part of the coach actually swings out and the top tilts inwards but this is false economics, the CG is still being forced outwards not inwards (or down) so yes it may tilt but no gain.

There's an older suspension system on the net that actually has the front control arms crossing over each other (the lower BJ goes to the top pivot and vise versa) that prevents body roll and I have often toyed with the idea of that being ideal for a zero roll reverse trike especially to keep the rear tyre perpendicular - if I remember it's name .....

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